The manufacturing of slender products is carried out by extrusion, drawing and, more generally, by hot and/or cold longitudinal deformation. In an ideal condition, the site of the points connecting the section centres of a slender article, along the axial direction, should normally lie on a perfect straight line, but the technological issues for manufacturing cause this important condition to be obtainable only with a given level of approximation.
FIG. 1, which represents a slender article known per se, shows, by way of example, an article 18 having a round section 24, 25 (alternatively, the articles are also produced with hexagonal section, square section, etc.), wherein it is evident how the straightness axis 23 does not coincide with the site of the section centres 26; in this figure the view is very compressed in order to reduce the size of the image, but it should be noted that the curvilinear abscissa 26 is in the order of metres and the cross-sectional size is in the order of tens of millimetres, from which the slenderness of the article is resulting.
The geometric straightness condition of the article, whatever the geometric shape of the section is, is very important for subsequent processing aspects of the product, especially if the article is rotated at high speed along its main axis. The straightness is defined by standards (refer to FIG. 1) as the maximum deviation 22 of the arc 26 from the baseline 23; the perfect straightness (practically only theoretical) is reached when the actual points of the article 26 coincide with the points of the theoretical axis 23 and consequently the deviation 22 is zero.
Given the complexity of realizing and achieving this geometrical condition, and given the need to guarantee a more and more rectilinear product for subsequent processing, being able to measure the residual deformation of the manufactured product is very useful, so as to perform both discarding activities of non-compliant products due to an excess of curvature, and the classification of intermediate quality products based on the obtained level of straightness. The residual tensile state in the product, downstream of the hot and/or cold processing, is the cause of the residual deformation thereof with respect to the condition of perfect straightness.
In the field of production of slender articles (typically, bars with different sections) there are regulations defining the acceptability fields of these articles based on materials they are made of, on size and on section geometry. These values are normally expressed in terms of sagitta (deviation), i.e. the maximum arc deviation with respect to a fixed-length baseline, and are quantified in the measurement unit of mm/m with the intent of representing the size of the sagitta with respect to a predetermined reference arc. The limit values of acceptability are the result of a compromise between the manufacturing problems and the need for subsequent processes.
Over the years, many manufacturers of systems and, more particularly, of measurement systems, have dedicated resources to define methodologies capable of automatically obtain measures that could be attributable to the values considered by the reference standards. The main known systems are based on measurement methods envisaging the step of rotating the slender article on fixed supports, thus determining the straightness values on the basis of the vertical position variations of the slender article detected in different points of the same or simply in a median position with respect to the above-mentioned points. Other systems are based on rolling principles of the article on inclined planes, with detecting and evaluating of points of contact with the plane during or after the rolling.
For the detection of the geometry of the slender article on various rolling systems, various measurement techniques have been adopted. The main techniques are of the mechanical type with contact, also known as feelers; of laser-optical type with punctual sensors or profilometres, of visual-optical type through the use of cameras with lens systems, even telecentric, or of electric type through the closure of electrical contacts placed in very precise positions.
The systems for the geometry detection of slender articles lying, during the measurement, on vertically fixed references, raises the limit of conditioning that the fixed support system exerts on the geometry of the slender article itself, making the measurement extremely inaccurate.
There are also more sophisticated systems which provide the geometry detection of the slender article on non-fixed support systems. The purpose of these, systems is to create compensations to the effect of gravity on the geometry to be detected. Systems of this type, which employ different suspension technologies, are known from EP 2057438, EP 1974179, EP 1915323, JP 063331339 and JP S5934109. None of these solutions of the prior art provide a system that is simple and reliable at the same time, but actually effective to support a slender body or article in a way substantially free of constraints affecting its actual natural shape.